linux-kernel - Re: [PATCH] [8/18] BKL-removal: Remove BKL from remote

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Message-Id: <1201475336.7346.37.camel@heimdal.trondhjem.org>
Date:	Sun, 27 Jan 2008 18:08:56 -0500
From:	Trond Myklebust <Trond.Myklebust@...app.com>
To:	Steve French <smfrench@...il.com>
Cc:	Andi Kleen <ak@...e.de>, swhiteho@...hat.com, sfrench@...ba.org,
	vandrove@...cvut.cz, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, akpm@...l.org
Subject: Re: [PATCH] [8/18] BKL-removal: Remove BKL from remote_llseek


On Sun, 2008-01-27 at 16:18 -0600, Steve French wrote:
> If two seeks overlap, can't you end up with an f_pos value that is
> different than what either thread seeked to? or if you have a seek and
> a read overlap can't you end up with the read occurring in the midst
> of an update of f_pos (which takes more than one instruction on
> various architectures), e.g. reading an f_pos, which has only the
> lower half of a 64 bit field updated?   I agree that you shouldn't
> have seeks racing in parallel but I think it is preferable to get
> either the updated f_pos or the earlier f_pos not something 1/2
> updated.

Why? The threads are doing something inherently liable to corrupt data
anyway. If they can race over the seek, why wouldn't they race over the
read or write too?
The race in lseek() should probably be the least of your worries in this
case.

Trond
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